Digital Voices – The Formats Presently Being Used in Public Safety and Amateur Radio
APCO P25 Phase I is the present version that is in used across the country for Digital Public Safety, the P25 “open” standard has been reworked by some manufacturers limiting some of the standardization that the P25 was hoped to present..
P25 Phase I has the ability to function as a analog system or digital system.
P25 Presently operates via FDMA (Frequency Division Multiple Access) with the plan for P25 Phase II to use TDMA (Time Division Multiple Access), P25 Phase II will also have the capability to “roll-back” to FDMA for “conventional emergency operations.”
D-STAR is a Amateur Radio system which offers digital voice and data communication. It connects repeater sites over microwave links and the Internet and forms a wide area Amateur Radio network.
The D-STAR system provides a new capability and functionality to the Amateur Radio world and increases the efficiency of emergency communications.
D-STAR provides digital voice at 4k8 baud and data is available via 1.2GHz at a rate up to 128kbps via GMSK modulation – Gaussian Mask Shift Keying,
On VHF and UHF digital voice plus 950bps data can coexist on the same channel.
At the present time only Icom is making transceivers with D-STAR capability. With experimentation one can modify other transceivers for D-STAR Connectivity.
Fixed Base (i.e. repeaters) do not have analog capabilities – Strictly Digital Only.
Mobile/Porable D-STAR enabled equipment have both analog and digital capabilities.
MotoTRBO(tm) MotoTRBO is a product of Motorola with the primary market being Industrial-Business Sector. MotoTRBO is designed to operate digital only on a single 12.5kHz channel by slicing the digital transmissions into time slots thus creating to available channels via TDMA (Time Division Multiple Access).
Data throughput is 2k0 per time slot.
MotoTRBO has analog capability (repeaters can be programmed to operate analog or digital, mobiles and portables can operate analog and digital).
NXDN was designed by Icom and Kenwood primarily for the Industrial-Business Sector.
NXDN is marketed by Icom as IDAS (Icom Digital Advanced System) and Kenwood as NEXEDGE. With channels at true 6.25kHz channel spacing using FDMA (Frequency Division Multiple Access).
NXDN provides 9k6 @ 8.3kHz bandwidth and 4k8 @ 4kHz bandwidth.
NXDN is compatible with analog systems thus making migration from analog to digital easier. Some of the companies participating in NXDN equipment development include: Daniel Electronics, Icom, Kenwood and Ritron among others.
Source: DARN SIMPLE